Locking nail for treating fractures of the proximal femur

ABSTRACT

An interlocking nail, particularly for fractures of the proximal femur having a proximal portion that has provided therein a bore preferably extending obliquely to the axis of the proximal portion for receiving a screw or pin, particularly a femoral neck pin. The bore is formed so that the lateral edge portions located on opposed sides are flattened and rounded at the inlet end or also the outlet end of the bore and continuously pass over into adjacent edge portions towards the proximal and distal sides of the inlet end and/or outlet end.

BACKGROUND OF THE INVENTION

[0001] The invention relates to an interlocking nail, particularly forfractures of the proximal femur.

[0002] For a repair of trochanteric fractures and fractures of thefemoral neck or femoral head, it is known to provide an interlockingnail which is driven into the femur from the proximal end and, in a anoblique through bore, guides a femoral neck pin which is introduced intothe femoral head via the femoral neck of the femur. It is known toprovide the femoral neck pin with a thread to allow it to be screwedinto the femoral head (femoral neck screw); however, it is also known todesign the femoral neck pin as a blade. In the proximal part of theinterlocking nail, it is further known to provide a bore which interactswith the femoral neck pin in such a way that it can axially move in theoblique through bore, but cannot rotate. Such a nail is shown in U.S.Pat. No. 5,176,681.

[0003] The weight force of a patient who is provided with such animplant is essentially directed into the interlocking nail from thefemoral neck pin. The nail cross-section, when under a load, issubjected to a combined stress which is composed of bending and tensilestresses. In case of an overload, a crack or fissure-may develop, namelyat the site at which the highest tensile stress occurs. The highestconcentration of stress results on the sharp lateral edges on opposedsides of the femoral neck pin when it is in the oblique through bore.Thus, the so-called fatigue strength of the implant depends on thecritical area having edges with a sharp-edged geometry. The highesttensile stresses occur at the screw inlet end of the bore.

SUMMARY OF THE INVENTION

[0004] It is one object of the invention to improve an interlocking nailof the aforementioned type by enhancing its fatigue strength.

[0005] In the interlocking nail of the present invention, the edgeslocated on opposed sides of the pin (when it is in the bore) areflattened or chamfered at the inlet end and/or outlet end of the bore.They are rounded and continuously pass over into the adjacent proximaland distal edge portions. It is preferred that the surface portionsdefined by the flattened edges in the distal and proximal end areas areformed to be essentially concave in a side view and are approximatelystraight in cross-section.

[0006] Regarding the individual edge portions at the inlet end of thebore, the edge portions directed towards the proximal and distal ends ofthe nail are discriminated from those which are located towards thesides of the nail. The latter are meant primarily with respect to theformation of surface portions. For known nails, the reason is that thoseedge portions constitute the most critical portions for a load becausethey are in an area of reduced cross-section. In the invention, somematerial is removed by chamfering in the area of these edge portions ina way that avoids a notch effect and, hence, the risk of stress peaksforming in this area. Load-bearing capacity increases although materialis removed. In addition, this essentially maintains the entire supportarea for the pin in the hole, particularly that of the femoral neck pinin the oblique through bore as is predetermined by the geometry of thenail and bore.

[0007] It is possible to provide for the removal of material byflattening or beveling exclusively in the aforementioned edge areas.However, according to an aspect of the invention, it is preferred that anotch be formed which bevels nearly the entire circumferential edge atleast of the inlet end, to define the flattened edge portions at theinlet end or outlet end of the bore. Also, it may be configured ingeometry so as to maintain the sliding surface of the pin essentiallyover the entire length.

[0008] Preferably, the outer rounded circumferential edge of the notchdefines a contour having rounded corners which essentially isrectangular or square.

[0009] The relatively narrow, elongate surface portions on the opposedlateral edge portions preferably pass over, towards the proximal anddistal sides of the inlet end or outlet end, into beveled or chamferedsurface portions which exhibit a concave run as seen from the side andpass over into the rounded outer edge in a rounded shape.

[0010] The invention is particularly useful for interlocking nails whichreceive a femoral neck pin in a proximal oblique hole. Also, theinventive relief of stress from the inlet end of the oblique hole issufficient here. However, it is also suited for holes of theinterlocking nail which are perpendicular to the nail axis and aredistally disposed.

[0011] In the nail of the present invention, the fatigue strength of theimplant is enhanced by varying the external geometry of the bore at theends so as to bypass the stresses provoked by the load when in aclinical use in order to relieve particularly critical areas as arisebecause of sharp-edged geometries. The sharp edges are removed and thestress is spread over a larger surface. This advantage is attained withno harm caused to the sliding mechanism for the pin.

[0012] As discussed above, the stress lines run along the weakestcross-section in a through bore of a nail. The fact that a flattening iseffected in the lateral edge portions of the inlet end of the obliquehole in the invention the stress lines are bypassed around thecross-section in the area of higher strength. Also, a provision can bemade here to chamfer or bevel the circumferential edge by the removal ofmaterial at the inlet end of the bore over its entire path. At thisstage, the invention provides for the circumferential edge of the inletarea to present a circumferential chamfer or inclined surface the shapeand run of which is formed by the fact that a circular milling cutter,which is rotated about its axis which is perpendicular to the axis ofthe proximal nail portion and the diameter of which is larger than thediameter of the bore, helps to move it against the edge of the inlet enduntil the circumferential chamfer is produced. In this manner, anefficient relief from stress is also achieved in the inlet end of thebore with the material not being unfavorably weakened or the supportsurface of the femoral neck pin or other pin in the bore beingdiminished. Thus, the step of manufacture, which is required to producethe stress reduction can be accomplished by simple means.

[0013] These and other objects of the invention are achieved by a nailfor insertion into the medullary canal of the long bone, such as afemur, which nail has an elongated shank extending along thelongitudinal axis from a first and to a second end of the nail shank. Across-bore extends through the nail shank along an axis transverse tothe longitudinal axis. The cross-bore is for receiving a bone fastener,such as a bone screw or a bone pin from an inlet side of the cross-boreto an outlet side thereof. When used in conjunction with the femur, thecross-bore may be at an oblique angle and extend through the proximalend of the nail into the head of the femur. An outer surface surroundingthe bore inlet end has recessed edges along first and second sidesthereof with at least central portions of the recessed edges beingsubstantially planar and extending in a plane generally parallel to thelongitudinal axis of the shank. Where the recessed edges intersect theedges of the throughbore, the sharp corners may be relieved such as byrounding or blending the recessed edge into the inner bore.

[0014] The recessed edges form first and second sides of a notch in theouter surface surrounding the bore with the first and second recessededges being connected by a third side of the notch with the third sideextending in a direction generally perpendicular to the nail axis.Preferably, the third side forms an arcuate chamfer from the outersurface surrounding the bore of the nail to the bore. When the nail is afemoral nail, the arcuate chamfer is located at least on the distal sideof the outer surface surrounding the bore. The first and second recessedsides are connected by a fourth side located closer to the first end ofthe nail, which, in the femur is the proximal end. The fourth side mayalso have an arcuate chamfer between the bore and the outer surface ofthe nail surrounding the bore. The first and second sides have portionswhich are parallel and, similarly, the third and fourth sides have edgeswhich are parallel to each other. Preferably, the parallel portions ofthe first and second sides are perpendicular to the parallel portions ofthe third and fourth sides.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The invention will be described in more detail below withreference to an embodiment shown in the drawings.

[0016]FIG. 1 shows the side view of an interlocking nail according tothe invention;

[0017]FIG. 2 shows a section through the nail of FIG. 1 along line 2-2;

[0018]FIG. 3 shows the enlarged plan view of some part of the nail ofFIG. 1;

[0019]FIG. 4 shows a plan view similar to FIG. 3, but from a perspectiveoffset by 90°;

[0020]FIG. 5 shows the side view of the nail portion of FIG. 3;

[0021]FIG. 6 shows a plan view of a proximal portion of a bone nailsimilar to the proximal portions of FIGS. 3 to 5 with an oblique throughbore according to the state of the art;

[0022]FIG. 7 shows the same view after making a chamfer on thecircumferential edge of the inlet end of the oblique bore shown; and

[0023]FIG. 8 shows a side view of the nail portion of FIG. 7

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] An interlocking nail 10 as is illustrated in FIGS. 1 and 2 has aproximal portion 12 and a distal portion 14. The latter contains anelongate cross-bore 16 for receiving an interlocking screw which is notshown. The proximal portion has an oblique through bore 18 for receivinga femoral neck pin which is not shown. Reference was made above and willalways be made below to a femoral neck pin although it is intended togenerally comprise all common femoral neck screws and pins that havebecome known up to this date.

[0025] The nail 12 is completely formed with an axial through bore 20and the proximal end has provided thereon two threaded portions 22, 24which are different in diameter, the internal one 24 serving for thereception of an interlocking pin or set screw, which is not shown, forthe femoral neck pin and the thread 22 serving for the reception of aninsertion and targeting instrument, which is not shown, for fixing thenail via the proximal femur. A radial recess 26 at the proximal endserves for orienting the insertion and targeting instrument on the nail10 in a rotary sense. These constructional features mentioned are knownin the state of the art. The description which follows is focused on theoblique bore 18. Bore 18 has an inlet end 30 and an outlet end 32 forthe femoral neck pin. The inlet end faces away from the head of thefemur when the nail has been driven into the femur proximally. Theconsiderations below exclusively refer to the inlet end which can berecognized in FIG. 1, but is depicted more distinctly in FIGS. 3 and 4.

[0026] As shown in the Figures the area of the inlet end 30, in a planview, has formed therein a notch the outer rounded edge 34 of which hasan approximately square contour with rounded corners. The edge 34 islocated in the outer contour of the proximal nail portion 12 and outsidethe edge which is formed by the bore 18. The inner edge of the notchwhich is radially located within the outer edge 34, which is formed bythe intersection with 18, is designated by 36. Surface portions whichpartially are beveled or chamfered are formed between the outer edge 34and the inner edge 36. First lateral surface portions 38, 40 are locatedon opposed sides of the femoral neck pin and, in a plan view, extendapproximately in parallel with the outside of proximal nail portion 12.As shown in FIG. 2 surface portions 38, 40 are located, at least intheir middle region, approximately in a common plane which extendsapproximately in parallel with the longitudinal axis of proximal nailportion 12. The surface portions 38, 40 continuously pass over intosurface portions 42, 44 in both the proximal and distal directions. Asshown in FIG. 3, surface portion 42 is distal and the surface portion 44is proximal. As can be seen from FIG. 2 the run of contour of thesurface portions 38, 40 is lightly concave in cross-section,particularly towards the ends, and the surface portions 38, 40continuously pass over into a surface portion which is formed by thebore 18 proximally. The outer proximal edge portion essentially matchesthe run of the edge portion which is formed by the bore 18 anyhow.

[0027] The described configuration or the notch to be made in theoblique hole 18 in the inlet area for the femoral neck pin can beproduced by a relatively easy manufacturing technique. The notch ensuresa marked reduction of the stress peaks in the end portions of the bore18 when the femoral neck pin in the bore 18 is loaded by the force ofthe patient's weight, specifically at the inlet end, with no noticeablereduction to the sliding surface of the femoral neck pin, i.e. thesupport surface for the femoral neck pin in the oblique bore 18. Theremoval of material from the inlet end 30 can be readily seen from FIG.5. The line of penetration of the oblique bore 18 in the outer contourof the proximal nail portion 12 has undergone a variation as seen fromoutlet end 32 because of the removal of material from and the chamferingof the edge areas of the inlet end 30. It can be appreciated thatrelatively little material was removed so that the weakening of thematerial is negligible and is greatly outweighed by the advantages offavorable force transfer into the nail from the femoral neck pin. It isthe surface portions 38, 40 which are vital for the reduction of thestress peaks.

[0028] FIGS. 6 to 8 illustrate a proximal nail portion 50, e.g. thatportion 12 of the femoral nail of FIGS. 1 and 2. FIGS. 6 and 7 each showthe upper end towards the top of the page facing end of the nail whereasthe lower end points towards the distal end. The oblique hole is alsoreferred to as 18. Likewise, the axial through bore is designated by thesame reference number 20 as in FIGS. 2 to 4. The direction of sight ofthe lateral views of FIGS. 6 and 7 is perpendicular to the naillongitudinal axis. FIG. 6 shows the nail portion 50 immediately afterthe manufacture of the oblique through bore and axial through bore 20.FIG. 7 shows the deformation of the circumferential edge 52 of the inletend for a femoral neck pin and is introduced into the oblique bore 18after undergoing chamfering or flattening by a milling cutter as thiswill be described below with reference to FIG. 8.

[0029]FIG. 8 shows the side view of the nail portion 50 approximatelyperpendicular to the oblique through bore 18 with the nail portion 50having been rotated clockwise by about 5°, however. This allows a clearview of the run of edge 52 at inlet end 54 of the oblique bore 18. FIG.8 further shows a circular milling cutter 56 which is rotated about anaxis which is perpendicular to the longitudinal axis of the nail portion50. The axial extension of the milling cutter 56 is larger than is thediameter of the oblique bore 18. The diameter of the circular millingcutter 56 is also larger than is the diameter of the oblique bore 18.During machining, the milling cutter is moved towards the edge 52 in thedirection of the arrow 58. At this point, the milling cutter 56 plungesinto the inlet end 54 of the bore approximately centrally and chamfersthe circumferential edge 54 circumferentially as can be seen at 60 inFIG. 7. Also here, in particular, lateral opposed surface portions 38,40 are formed which bevel or chamfer the edge portions of thecircumferential edge 52 in this area in order to lower the stress peaksin this area of the nail portion. The cutter 56 can be moved in adirection parallel to the nail longitudinal axes to produce flattenedlateral edges.

[0030] A similar surface preparation may be performed on outlet end 32of bore 18.

[0031] Although the invention herein has been described with referenceto particular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the appended claims.

1. An interlocking nail, particularly for fractures of the proximalfemur comprising a proximal portion having a longitudinal axis having abore extending transverse to the axis of the proximal portion forreceiving a screw or pin, the bore having lateral edge portions locatedon opposed sides of the bore which are flattened and rounded at a screwor pin inlet end which edge portions continuously pass over intoadjacent edge portions towards the sides of the bore aligned with saidaxis at the bore inlet end.
 2. The interlocking nail as set forth inclaim 1 wherein the surface portions formed by the flattened edgeportions essentially extend concavely in the end region in thelongitudinal direction of the nail portion.
 3. The interlocking nail asset forth in claim 1 wherein a notch is formed to define the flattenededge portions at the bore inlet end.
 4. The interlocking nail as setforth in claim 3 wherein in that the notch is of such a shape that thesliding surface of the pin in the bore is maintained essentially overthe entire length of the original bore.
 5. The interlocking nail as setforth in claim 4 wherein the circumferential outer edge of the notchwhich is rounded in cross-section has an approximately rectangular orsquare contour.
 6. The interlocking nail as set forth in claim 1 whereinthe lateral surface portions extending to be approximately axiallyparallel, in a middle region in the direction of the longitudinal axisand are located approximately in a common plane which extendsapproximately in parallel to the longitudinal axis.
 7. The interlockingnail as set forth in claim 6 wherein a proximal end of the lateralsurface portions of the notch are rounded to pass over into a surfaceportion concave in cross-section a radially outer edge portion of whichdefines the proximal outer edge portion of the notch.
 8. Theinterlocking nail as set forth in claim 7 wherein a distal end of thelateral surface portions of the notch are rounded and pass over into aconcave surface portion extending crosswise to the nail axis whichoutwardly passes over into the outer contour of the nail approximatelyin parallel with the axis of the bore via a rounded edge.
 9. A methodfor manufacturing an interlocking nail, particularly for fractures ofthe proximal femur having a proximal portion with a longitudinal axis,said proximal portion having a bore extending obliquely to the axis ofthe proximal nail portion for receiving a screw or pin, particularly afemoral neck pin, the method comprising: forming an edge of an inlet endof the bore with a circumferential chamfer the shape and run of whichare defined by using a circular milling cutter which rotates about anaxis perpendicular to the axis of the proximal portion and which has anouter diameter which is larger than a diameter of the bore and movingthe cutter approximately centrally against the inlet end and against theedge of the inlet end approximately perpendicularly to a longitudinalaxis of the proximal nail portion until the circumferential chamfer hasbeen produced.
 10. A nail for insertion into the medullary canal of along bone comprising: an elongated shank extending along a longitudinalaxis from a first end to a second end of said shank; a bore extendingthrough the shank along an axis transverse to said longitudinal axis forreceiving a bone fastener, said bore having an inlet end into which thebone fastener is inserted, an outer nail surface surrounding said boreinlet end having recessed edges along first and second sides thereofsaid recessed edges being substantially planar and extending in a planegenerally parallel to the longitudinal axis of said shank.
 11. The nailas set forth in claim 10 wherein said recessed edges form first andsecond sides of a notch in the outer surface surrounding said bore, saidrecessed edges are connected by a third side of the notch, said thirdside extending in a direction generally perpendicular to said nail axis.12. The nail as set forth in claim 11 wherein said third side forms anarcuate chamfer from the outer surface surrounding said bore of saidnail to the bore.
 13. The nail as set forth in claim 12 wherein saidnail is a femoral nail, said first end being a proximal end and saidarcuate chamfer located on a side of said bore closer to said secondnail end.
 14. The nail as set forth in claim 13 wherein said recessededges are connected by a fourth side located closer to said first end.15. The nail as set forth in claim 14 wherein said fourth side forms anarcuate chamfer between the bore and the outer surface of the nailsurrounding said bore.
 16. The nail as set forth in claim 15 whereinsaid third and fourth sides are parallel and said first and second sidesare parallel.
 17. The nail as set forth in claim 10 wherein an edge ofeach of said recessed edges adjacent said bore is rounded into saidbore.